Introduction to instrumentation system
The instrument :
Sensors:
It is a device which sense the value of the process variable.
Five sensory organs of human body that provides data to our brain for perception :
Ear
Nose
Eye
Skin
Tongue
Useful sensors:
Flow rate
Pressure
Temperature
Oxygen
Torque
Position sensor
Transducer:
Transduction means conversation of input information into suitable form for output
Actuator :
It is a device which converts controlled signal to action signal
Active sensor:
Active sensor are self powering devices and do not require an external power supply for sensing
Example: thermocouple, solar cell , piezoelectric effect
Passive sensor:
Passive sensor not self generating type and require an external power supply for sensing
Example: thermister
Characteristics of transducers :
Range
The range conveys the information about the lower and upper limit values of the measurands
Error
The algebraic difference between the measured value (M) and actual or true value (T) of a measurands is defined as error (E)
Thus E = M - T
Accuracy
% inaccuracy = (error ÷ true value)×100
Precision
It is a measure of the reproducibility of the measurements
Linearity
One of the important characteristics of sensor is linearity i.e the output should be linearly proportional to the input
Resolution
It is defined as the smallest incremental change in the input that would produce a detectable change in the output
Reproducibility
Is the ability of sensor to produce output readings when the same input is applied at different times under different conditions and by different instruments
Sensitivity
It define as the ratio of the changes in the output of a sensor to a change in a value of the measurands
It is given by
S = ∆y÷∆x
Selected criteria for sensors:
Purpose of measurement.
Source of measurands
Range of measurands
Ambient conditions
Life span of sensor
Transduction principal
Availability of sensors
Ease of operation
Cost
Related searches:
Instrumentation system
Electronic information
Instrumentation
Sensors
Transducer
Characteristics of transducer
Active sensors
Passive sensors